1. Field of the Invention
The present invention relates to a display device. Specifically, the present invention relates to an active matrix display device provided with a transistor which is provided in each pixel and includes a channel formed in an oxide semiconductor layer.
2. Description of the Related Art
Since display devices using light-emitting elements have high visibility, are suitable for reduction in thickness, and do not have limitations on viewing angles, they have attracted attention as display devices which can take the place of CRTs (cathode ray tubes) or liquid crystal display devices. Specifically proposed structures of active matrix display devices using light-emitting elements are different depending on manufacturers. However, in general, at least a light-emitting element, a transistor which controls input of video signals to pixels, and a transistor (a driving transistor) which controls current supplied to the light-emitting elements are provided in each pixel.
When all the transistors in pixels have the same polarity, it is possible to reduce the number of manufacturing steps of the transistors. Patent Document 1 discloses a display device in which transistors included in pixels are all n-channel transistors.